Fitness and activity monitors typically take the form of a small display device that is worn as a wristwatch or, in the case of a bicycle computer, motorbike, or snowmobile speedometer, mounted to the handlebars of the vehicle. Performance metrics such as heart rate, speed, distance, location, cadence, power, among others, are measured by one or more sensors connected to the display device either electrically or through a wireless communication link. The display device typically receives, processes, and displays the performance information to the user.
Such activity monitors and feedback mechanisms may present several issues to the user. First, since the display device must be lightweight and portable, the display size is typically small and difficult to read while in motion, a situation that is worsened in low light conditions. In certain sports, such as swimming, it is not feasible for the user to read a display without significantly interfering with the activity. Second, the user must frequently take focus off of his activity to read displayed information, which can be distracting or dangerous to the activity at hand. Competitive athletes can find such a lack of focus detrimental to optimal performance and safety. Certain activities such as cycling, motorcycling, and snowmobiling require constant attention to the road, trail, and surrounding environment; looking elsewhere can lead to injury. Third, the reading and operation of a wrist-worn or handlebar-mounted display can interfere with efficient body motions required for optimal performance. Frequent viewing of a wristwatch, or operation of the wristwatch by the opposite hand, for example, can interfere with the efficient arm and corresponding stride motion during running activity. As another example, the viewing or operation of a bicycle computer can cause the cyclist to exit from a streamlined aerodynamic position, which is detrimental to his resultant performance.
Heads-Up displays, as well known in the art, present a focused image (e.g., alphanumeric characters and/or graphics) to a wearer of the display. The focused image is projected into at least part of the wearer's normal operational field of view, such that the user typically sees the focused image overlaid onto that normal field of view. While allowing the user to assimilate the information from the focused display, this information is also distracting since this focused image partially covers the wearer's operational field of view, that part of the wearer's normal field of view is obscured.